ii SENSIBILITY OF THE INTERNAL ORGANS 121 



nerve -endings of the ampullae and maculae of the labyrinthine 

 saccules, and of producing the sensory and .motor phenomena we 

 have been discussing. 



According to Mach, both in rectilinear and in angular and 

 rotatory movements, the endolymph presses on the wall opposite 

 to the direction of the movement. At each variation in the rate 

 of the movement there is a variation in the pressure, and a con- 

 sequent variation in the stimulation of the ampullary cristae in 

 the plane of which the movement takes place. 



The motor reactions produced by experimental labyrinthine 

 sensations are reflex phenomena of a compensatory character, which 

 tend to compensate the real or illusory effects of rotation or recti- 

 linear displacement. 



In the static position, according to Breuer, it is not the cristae 

 but the maculae of the saccules that are excited by the gravity of 

 the otolith. As the otoliths have a higher specific gravity than 

 the endolymph in which they are bathed, the hairs of the sensory 

 cells must be pulled in a different direction from that of the 

 position of the head ; this produces the excitations which give rise 

 to the sensation of this position in respect of the line of gravity, 

 and the reflex movements of the eye that are co-ordinated with it. 



According, therefore, to the theory of Breuer, Mach, and Crum 

 Brown, the labyrinth is composed of three distinct sense-organs : 

 the cochlea with the organ of Corti, for which the adequate 

 physiological stimulus consists in sound- vibrations ; the canals 

 with the cristae acusticae, which are physiologically stimulated by 

 the movements of the head; the vestibular saccules with the 

 maculae, the stimulus of which is the movement of the otoliths, 

 and particularly the variations in the rate of the rectilinear move- 

 ments, both on the horizontal and on the vertical planes. The 

 cochlea is the organ of hearing, as we shall see below ; the canals 

 are the organs on which depend the experimentally produced 

 sensations of rotatory and galvanic vertigo, and which normally 

 influence the complicated function of equilibration by means of 

 obscure sensations ; the saccules are the organs on which the sub- 

 conscious sensations that we normally have of the direction of the 

 line of gravity, and thus of the position of our body in relation to 

 the environment, depend. 



This ingenious theory accounts for nearly all the phenomena 

 described in the various experimental researches carried out on 

 the labyrinth of vertebrates from Flourens to Goltz, Goltz to 

 Breuer, Mach, and Crum Brown. But before we accept it uncon- 

 ditionally it is necessary to refer to another important series of 

 experiments on the labyrinth that have added greatly to our 

 knowledge of this important sense-organ, and enlarged the con- 

 ception of their functional significance. 



Ewald (1887-89, 1892-6) undertook an experimental study of 



